Electrolyte additive and use thereof

Abstract

An electrolyte additive and the use thereof. The electrolyte additive comprises an imidazole sulfonate compound, pentaerythritol bicyclic sulfate and 1,6-diisocyanatohexane.

Description

Electrolyte additive and application thereof

[0001] Priority information

[0002] The present disclosure claims priority to and the benefit of the patent application with the patent application number 2024113534157 filed with the China National Intellectual Property Bureau on September 26, 2024, and incorporates it herein in its entirety by reference. TECHNICAL FIELD

[0003] The present disclosure belongs to the technical field of energy, in particular relates to an electrolyte additive and application thereof, more particularly relates to an electrolyte additive, an electrolyte and a secondary battery. BACKGROUND

[0004] During the charging and discharging process of the secondary battery, the positive active material and the negative active material are prone to produce structural defects after the side reaction with the electrolyte, thereby causing the performance of the secondary battery to deteriorate. At present, on the one hand, the performance of the secondary battery is improved by improving the performance of the positive material and / or the negative material itself, and on the other hand, the stability of the electrolyte is improved to improve the comprehensive performance of the secondary battery.

[0005] The prior art mainly improves the stability of the electrolyte by adding an electrolyte additive to the electrolyte, but the existing electrolyte additive has limited performance improvement on the electrolyte, which limits the improvement of the performance of the secondary battery.

[0006] DISCLOSURE

[0007] The present disclosure provides an electrolyte additive, which can inhibit the free acid generated during the storage of the electrolyte such as transportation when used in the electrolyte, improve the stability of the electrolyte, and when the obtained electrolyte is applied to a secondary battery, the film forming resistance is low, which is conducive to improving the high temperature performance of the secondary battery.

[0008] The present disclosure provides an electrolyte comprising the above-mentioned electrolyte additive, which has stable acid value before and after storage, and when applied to a secondary battery, the film forming resistance is low, which can effectively improve the high temperature performance of the secondary battery.

[0009] The present disclosure provides a secondary battery comprising the above-mentioned electrolyte, so that the secondary battery has excellent high temperature performance.

[0010] The present disclosure provides an electrolyte additive, wherein the electrolyte additive comprises an imidazole sulfonate compound, a pentaerythritol bis-cyclic sulfate and 1,6-hexane diisocyanate.

[0011] According to some embodiments of the present disclosure, the imidazole sulfonate compound comprises a compound represented by Formula 1;

[0012] In Formula 1, R1 is selected from the group consisting of hydrogen, a substituted or unsubstituted C6-C18 aryl group, a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted thienyl group, a substituted or unsubstituted imidazolyl group, a substituted or unsubstituted pyridyl group, a group represented by Formula 2.

[0013] In Formula 2, R2, R3, R4 are each independently selected from the group consisting of hydrogen, halogen, a substituted or unsubstituted C1-C10 alkyl group.

[0014] According to some embodiments of the present disclosure, R1 is selected from the group consisting of hydrogen, a phenyl group, a thienyl group, an imidazolyl group, a pyridyl group, a fluorophenyl group, a fluorothienyl group, a fluoroimidazolyl group, a fluoropyridyl group, a methyl group, an ethyl group, a 1-propyl group, a 2-propyl group, a 1-butyl group, a 2-methyl-1-propyl group, a 2-butyl group, a fluoromethyl group, a fluoroethyl group, a fluoro-1-propyl group, a fluoro-2-propyl group, a fluoro-1-butyl group, a fluoro-2-methyl-1-propyl group, a fluoro-2-butyl group, a vinyl group, a propenyl group, a butenyl group, a fluorovinyl group, a fluoropropenyl group, a fluorobutenyl group, a trimethylsilyl group, a triethylsilyl group, a trifluorosilyl group, a (trifluoromethyl)dimethylsilyl group, a di(trifluoromethyl)methylsilyl group, a tri(trifluoromethyl)silyl group, a silylphenyl group.

[0015] According to some embodiments of the present disclosure, the imidazole sulfonate-based compound is selected from the group consisting of compounds represented by the following structures:

[0016] According to some embodiments of the present disclosure, in the electrolyte additive, the mass ratio of the imidazole sulfonate-based compound to the 1,6-hexane diisocyanate is (0.001-100):1.

[0017] According to some embodiments of the present disclosure, in the electrolyte additive, the mass percentage of the pentaerythritol bis-cyclic sulfate is 0.3%-3%.

[0018] The present disclosure provides an electrolyte comprising the electrolyte additive as described above.

[0019] According to some embodiments of the present disclosure, in the electrolyte, the mass percentage of the electrolyte additive is 0.36%-18%.

[0020] According to some embodiments of the present disclosure, the electrolyte further comprises an electrolyte salt and a solvent.

[0021] According to some embodiments of the present disclosure, the electrolyte comprises, by mass fraction, 7-18% of electrolyte salt, 65-88% of solvent, 0.01-5% of imidazolium sulfonate compound, 0.05-10% of 1,6-hexane diisocyanate, and 0.3-3% of pentaerythritol bis-cyclic sulfate.

[0022] According to some embodiments of the present disclosure, the electrolyte further comprises an auxiliary agent.

[0023] According to some embodiments of the present disclosure, the auxiliary agent is at least one selected from 1,3-propane sulfite, 1,3-propylene sulfite, fluoroethylene carbonate, bis-fluoroethylene carbonate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, triphenyl phosphate, triphenyl phosphite, succinic anhydride, dimethyl maleic anhydride, and methane disulfite.

[0024] According to some embodiments of the present disclosure, the auxiliary agent has a mass percentage content of ≤5% in the electrolyte.

[0025] According to some embodiments of the present disclosure, the electrolyte comprises, by mass fraction, 9-15% of electrolyte salt, 75-86% of solvent, 0.1-1% of imidazolium sulfonate compound, 0.1-2% of 1,6-hexane diisocyanate, 0.3-1% of pentaerythritol bis-cyclic sulfate, and 0.2-2% of auxiliary agent.

[0026] The present disclosure provides a secondary battery comprising the electrolyte as described above.

[0027] The electrolyte of the present disclosure has a simple composition of electrolyte additives, and when applied to an electrolyte, can inhibit the free acid generated during storage of the electrolyte during transportation and the like, improve the stability of the electrolyte, and obtain an electrolyte with low film-forming impedance, which is conducive to the high-temperature performance of the secondary battery.

[0028] The electrolyte of the present disclosure comprises the electrolyte additives described above, and the electrolyte has stable acid value before and after storage, low film-forming impedance when applied to a secondary battery, and can effectively improve the high-temperature performance of the secondary battery.

[0029] The secondary battery of the present disclosure comprises the electrolyte described above, and therefore has excellent high-temperature performance. DETAILED DESCRIPTION

[0030] In order to make the objectives, technical solutions and advantages of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be described clearly and completely below in conjunction with the embodiments of the present disclosure. Obviously, the described embodiments are only some of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the scope of the present disclosure.

[0031] The first aspect of the present disclosure provides an electrolyte additive, the electrolyte additive comprising an imidazole sulfonate compound, a pentaerythritol bis-cyclic sulfate (TDT) and 1,6-hexane diisocyanate (HDI).

[0032] In the present disclosure, the imidazole ring in the imidazole sulfonate compound has a high electron cloud density, so that the imidazole sulfonate compound is more easily reduced in the redox reaction, generating an SEI film that is beneficial to the protection of the negative electrode; the imidazole sulfonate compound has strong electrophilicity and a high redox film-forming potential, while the pentaerythritol bis-cyclic sulfate has strong nucleophilicity; in this case, the imidazole sulfonate compound is more likely to attack the carbon atoms of 1,6-hexane diisocyanate, and preferentially react with 1,6-hexane diisocyanate to generate an imidazole group-containing sulfonylisocyanate compound; the imidazole group-containing sulfonylisocyanate compound not only can reduce the problem of rising acid value and color of the electrolyte caused by decomposition of electrolyte salts due to trace moisture (for example, the decomposition of hexafluorophosphate generates HF and PF5, thereby causing the acid value and color of the electrolyte to rise); but the sulfonylisocyanate group in the sulfonylisocyanate compound can significantly reduce the film-forming resistance of the pentaerythritol bis-cyclic sulfate when participating in the redox reaction, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery. Therefore, the electrolyte additive of the present disclosure can improve the high-temperature performance of the secondary battery.

[0033] In some embodiments of the present disclosure, the imidazole sulfonate compound comprises a compound represented by Formula 1;

[0034] In Formula 1, R1 is selected from hydrogen, a substituted or unsubstituted C6-C18 aryl group, a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted thienyl group, a substituted or unsubstituted imidazolyl group, a substituted or unsubstituted pyridyl group, and a group represented by Formula 2.

[0035] In Formula 2, R2, R3 and R4 are each independently selected from hydrogen, halogen, a substituted or unsubstituted C1-C10 alkyl group.

[0036] Specifically, in Formula 1, R1is selected from the group consisting of hydrogen, a substituted or unsubstituted C6-C18 aryl group (e.g., phenyl, substituted phenyl), a substituted or unsubstituted C1-C10 alkyl group (e.g., the alkyl group can be a straight chain alkyl group, a branched alkyl group, a cyclic alkyl group), a substituted or unsubstituted C2-C10 alkenyl group (e.g., a straight chain alkenyl group, a cyclic alkenyl group (e.g., a cyclopentadiene group with or without a heteroatom)), a substituted or unsubstituted thienyl group (e.g., a substituted thienyl group, a thienyl group), a substituted or unsubstituted imidazolyl group (e.g., a substituted imidazolyl group, an imidazolyl group), a substituted or unsubstituted pyridyl group (e.g., a pyridyl group, a substituted pyridyl group), a group represented by Formula 2;

[0037] Specifically, in Formula 2, R2, R3, R4are each independently selected from the group consisting of hydrogen, a halogen (e.g., F, Cl, Br, I), a substituted or unsubstituted C1-C10 alkyl group (e.g., the alkyl group can be a straight chain alkyl group, a branched alkyl group, a cyclic alkyl group).

[0038] The present disclosure does not limit the types of substituents of the alkenyl group, the alkyl group, the thienyl group, the imidazolyl group, the pyridyl group, and the aryl group, and can be a substituent commonly used in the art, for example, can be at least one of a halogen, a cyano group, an ester group, a nitro group, an amino group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted alkoxy group, an isocyano group, an isocyanate group, and a substituted or unsubstituted aryl group.

[0039] In some embodiments of the present disclosure, when the imidazole sulfonate-based compound includes a compound represented by Formula 1, the imidazole sulfonate-based compound can more effectively bind to the isocyanate group in 1,6-hexamethylene diisocyanate, further neutralize the acid value, and can obtain a compound having a low film formation resistance, improve the storage stability of an electrolyte, and thus improve the high-temperature performance of a secondary battery.

[0040] Further, when R1is selected from the group consisting of hydrogen, a phenyl group, a thienyl group, an imidazolyl group, a pyridyl group, a fluorinated phenyl group, a fluorinated thienyl group, a fluorinated imidazolyl group, a fluorinated pyridyl group, a methyl group, an ethyl group, a 1-propyl group, a 2-propyl group, a 1-butyl group, a 2-methyl-1-propyl group, a 2-butyl group, a fluorinated methyl group, a fluorinated ethyl group, a fluorinated 1-propyl group, a fluorinated 2-propyl group, a fluorinated 1-butyl group, a fluorinated 2-methyl-1-propyl group, a fluorinated 2-butyl group, a vinyl group, a propenyl group, a butenyl group, a fluorinated vinyl group, a fluorinated propenyl group, a fluorinated butenyl group, a trimethylsilyl group, a triethylsilyl group, a trifluorosilyl group, a (trifluoromethyl)dimethylsilyl group, a di(trifluoromethyl)methylsilyl group, a tri(trifluoromethyl)silyl group, a silylphenyl group, the high-temperature performance of a secondary battery can be further improved.

[0041] Exemplarily, the imidazole sulfonate-based compound is selected from the group consisting of compounds represented by the following structures:

[0042] In some embodiments of the present disclosure, the electrolyte additive comprises imidazole sulfonate compounds, 1,6-hexane diisocyanate, and pentaerythritol bis-cyclic sulfate. It is understood that the content of imidazole sulfonate compounds, 1,6-hexane diisocyanate, and pentaerythritol bis-cyclic sulfate has a crucial impact on the performance of the electrolyte additive, and therefore the content of imidazole sulfonate compounds, 1,6-hexane diisocyanate, and pentaerythritol bis-cyclic sulfate can be selected to further improve the performance of the electrolyte additive.

[0043] For example, in some embodiments of the present disclosure, when the mass ratio of imidazole sulfonate compounds to 1,6-hexane diisocyanate in the electrolyte additive is (0.001-100):1 (specifically, 0.01:1, 0.1:1, 1:1, 10:1, 50:1, 100:1, etc.), the imidazole sulfonate compounds can react more fully with 1,6-hexane diisocyanate to generate imidazole group-containing sulfonate isocyanate compounds, thereby increasing the content of imidazole group-containing sulfonate isocyanate groups in the electrolyte system, and further improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0044] Further, the mass ratio of imidazole sulfonate compounds to 1,6-hexane diisocyanate in the electrolyte additive is (0.05-10):1 (specifically, 0.05:1, 0.1:1, 1:1, 2:1, 4:1, 6:1, 8:1, 10:1, etc.).

[0045] In some embodiments of the present disclosure, when the mass percentage content of pentaerythritol bis-cyclic sulfate in the electrolyte additive is 0.3%-3% (specifically, 0.3%, 1%, 1.5%, 2%, 2.5%, 3%, etc.), the sulfonate isocyanate groups in the sulfonate isocyanate compounds can further reduce the film-forming resistance of pentaerythritol bis-cyclic sulfate when participating in the redox reaction, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0046] In the present disclosure, imidazole sulfonate compounds, 1,6-hexane diisocyanate, and pentaerythritol bis-cyclic sulfate are used together, and the sulfonate isocyanate groups in the sulfonate isocyanate compounds can further reduce the film-forming resistance of pentaerythritol bis-cyclic sulfate when participating in the redox reaction, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery. The specific reasons can be as follows:

[0047] (1) Electron transfer and SEI film optimization:

[0048] The sulfur atom (S) and the nitrogen atom (N) in the sulfonylisocyanate group have high electronegativity, and are prone to accept electrons to form a radical intermediate in the redox process. This characteristic enables it to be preferentially decomposed at a lower potential than the electrolyte solvent to generate stable SEI film components containing sulfur / nitrogen (such as Li2SO3, Li3N, etc.), thereby reducing the negative electrode interface impedance, and the sulfate group (-OSO2-) of pentaerythritol bicyclic sulfate further contributes to the sulfur source through synergistic reduction, enhancing the compactness and ionic conductivity of the SEI film.

[0049] (2) High-temperature stability is enhanced:

[0050] The sulfur / nitrogen-containing compounds (such as Li2SO4, Li2S) generated by the decomposition of the sulfonylisocyanate group have high thermal stability, which can inhibit the decomposition of the SEI film at high temperatures. At the same time, the synergistic effect of the sulfonylisocyanate group and the pentaerythritol bicyclic sulfate can reduce the oxygenation side reactions of the electrolyte and reduce the gas production (such as CO2, H2) during high-temperature storage.

[0051] (3) Interface kinetics is improved:

[0052] The sulfonylisocyanate group binds to the active sites on the electrode surface through nucleophilic attack, forming a uniform passivation layer and reducing the interface polarization during lithium ion deintercalation. The cyclic structure of pentaerythritol bicyclic sulfate limits side reactions through steric hindrance effects, and together improves the DCR stability during the cycle process.

[0053] (4) Additive synergistic effect

[0054] The introduction of the sulfonamide component (-SO2NH-) in the sulfonylisocyanate composition can further stabilize the isocyanate group and prevent performance degradation caused by decomposition during storage. This stability ensures its sustained effect in long-term cycling of the battery.

[0055] The second aspect of the present disclosure provides an electrolyte comprising the electrolyte additive of the first aspect.

[0056] The electrolyte of the present disclosure, due to the inclusion of the electrolyte additive of the first aspect, has stable acid value before and after storage, and when applied to a secondary battery, has low film-forming impedance, which can effectively improve the high-temperature performance of the secondary battery.

[0057] In some embodiments of the present disclosure, when the mass percentage of the electrolyte additive in the electrolyte is 0.36% to 18% (specifically, 0.36%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, etc.), the electrolyte additive can fully play its role without degrading the ion transport performance of the electrolyte, thereby improving the stability of the electrolyte, reducing the film formation impedance of the electrolyte, and further improving the high-temperature performance of the secondary battery. Further, the mass percentage of the electrolyte additive in the electrolyte is 0.5% to 6%. In this way, the stability of the electrolyte can be further improved, the film formation impedance of the electrolyte can be reduced, and the high-temperature performance of the secondary battery can be further improved.

[0058] It can be understood that the electrolyte further includes an electrolyte salt and a solvent.

[0059] The present disclosure does not make special limitations on the electrolyte salt, which can be a commonly used electrolyte salt in the art. The electrolyte salt can be a sodium salt or a lithium salt. When the electrolyte salt is a sodium salt, the obtained electrolyte can be applied to prepare a sodium ion battery. When the electrolyte salt is a lithium salt, the obtained electrolyte can be applied to prepare a lithium ion battery. In some embodiments, the sodium salt can include at least one of sodium hexafluorophosphate, sodium perchlorate, sodium bis(oxalato)borate, sodium difluoro(oxalato)borate, sodium bis(trifluoromethylsulfonyl)imide, and sodium bis(fluorosulfonyl)imide; and the lithium salt can include at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0060] The present disclosure does not make special limitations on the solvent, which can be a commonly used solvent in the art. In some embodiments, the solvent can be a non-aqueous organic solvent, which can include a carbonate compound and / or a carboxylic acid ester compound.

[0061] The present inventor found in the research that, by further selecting the contents of the electrolyte salt, the solvent, the imidazole sulfonate compound, the pentaerythritol bis-cyclic sulfate, and the 1,6-hexane diisocyanate in the electrolyte, the imidazole sulfonate compound, the pentaerythritol bis-cyclic sulfate, and the 1,6-hexane diisocyanate in the electrolyte additive can fully play their roles, and an electrolyte with more excellent comprehensive performance can be obtained.

[0062] For example, in some embodiments of the present disclosure, the electrolyte comprises, by mass fraction, 7% to 18% (specifically, 7%, 9%, 10%, 12%, 14%, 16%, 18%, etc.) of electrolyte salt, 65% to 88% (specifically, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, etc.) of solvent, 0.01% to 5% (specifically, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, etc.) of imidazole sulfonate compound, 0.05% to 10% (specifically, 0.05%, 0.1%, 0.5%, 1%, 2%, 5%, 8%, 10%, etc.) of 1,6-hexane diisocyanate, and 0.3% to 3% (specifically, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, etc.) of pentaerythritol bis-cyclic sulfate, which can further improve the high-temperature performance of the secondary battery.

[0063] In some embodiments of the present disclosure, the electrolyte further comprises an additive.

[0064] In some embodiments, when the additive is selected from at least one of 1,3-propane sulfone, 1,3-propylene sulfone, fluoroethylene carbonate, bis-fluoroethylene carbonate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, triphenyl phosphate, triphenyl phosphite, succinic anhydride, dimethyl maleic anhydride, and methane disulfonate methylene, the high-temperature performance of the secondary battery can be further improved.

[0065] Further, when the additive is selected from 1,3-propane sulfone and / or fluoroethylene carbonate, the high-temperature performance of the secondary battery is further improved.

[0066] In some embodiments of the present disclosure, when the mass percentage of the additive in the electrolyte is ≤5%, the additive can fully play its role, improve the comprehensive performance of the electrolyte, and further improve the high-temperature performance of the secondary battery. Further, the mass percentage of the additive in the electrolyte is 0.2% to 2% (specifically, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, etc.). Thus, the additive participates in the basic film formation, which is conducive to the cycle and storage performance of the battery.

[0067] Further, when the electrolyte comprises, by mass fraction, 9% to 15% of electrolyte salt, 75% to 86% of solvent, 0.1% to 1% of imidazole sulfonate compound, 0.1% to 2% of 1,6-hexane diisocyanate, 0.3% to 1% of pentaerythritol bis-cyclic sulfate, and 0.2% to 2% of additive, the components in the electrolyte can be more fully matched, the stability of the electrolyte is improved, the film formation impedance of the electrolyte is reduced, and the high-temperature performance of the secondary battery is further improved.

[0068] The third aspect of the present disclosure provides a secondary battery comprising the electrolyte of the second aspect.

[0069] It can be understood that the secondary battery further comprises a positive electrode sheet, a negative electrode sheet, a separator and an outer package. In a specific embodiment, the positive electrode sheet, the separator and the negative electrode sheet can be sequentially stacked to form an electrode core with a stacked structure, or sequentially stacked and then wound to form an electrode core with a wound structure, and then the electrode core is placed in the outer package, the electrolyte is injected into the outer package, and after sealing, the secondary battery is formed.

[0070] The secondary battery of the present disclosure can be a lithium ion battery or a sodium ion battery.

[0071] When the secondary battery is a lithium ion battery, the working voltage of the lithium ion battery can be 2.5V-4.5V, wherein the positive electrode active material in the positive electrode sheet can include LiNi 1-x-y-z Co x Mn y Al z O2, lithium nickel manganese oxide, lithium cobalt oxide, lithium-rich manganese-based solid solution, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, and 0≤x+y+z≤1; the negative electrode active material in the negative electrode sheet can include one or more of artificial graphite, lithium metal, coated natural graphite, silicon-carbon negative electrode, silicon negative electrode.

[0072] When the secondary battery is a sodium ion battery, the working voltage of the sodium ion battery can be 1.5V-4.2V, and the positive electrode active material in the positive electrode sheet can include Na x1 M1O2, Na x2 M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3, Na2M4(SO4)2·2H2O, wherein: 0

[0073] The secondary battery of the present disclosure comprises the above-mentioned electrolyte, and therefore the secondary battery has excellent high-temperature performance.

[0074] Hereinafter, the electrolyte of the present disclosure and its application are described in detail through specific embodiments.

[0075] Example 1

[0076] The sodium ion battery of the present embodiment is prepared by a method comprising the following steps:

[0077] (1) Preparation of the positive electrode sheet

[0078] The positive electrode active material Na[Ni 0.33 Fe 0.33 Mn 0.33 ]O2, the conductive agent carbon black, the carbon nanotube, polyvinylidene fluoride (PVDF), maleic acid, and N-methyl pyrrolidone (NMP) are added in a mass ratio of 94.5:2.5:1:1.8:0.2 to form a positive electrode slurry;

[0079] The positive electrode slurry is coated on the upper and lower surfaces of the aluminum foil, dried, and then cold-pressed. After edge cutting, sheet cutting, and striping, the positive electrode sheet is prepared.

[0080] (2) Preparation of the negative electrode sheet

[0081] The hard carbon, the conductive agent carbon black, the butadiene-styrene rubber (SBR), and the thickening agent (CMC) are added in a mass ratio of 95:1.5:2:1.5 in deionized water to form a negative electrode slurry. The negative electrode slurry is coated on the upper and lower surfaces of the aluminum foil, dried, and then cold-pressed, edge cut, sheet cut, and striped to prepare the negative electrode sheet.

[0082] (3) Preparation of the electrolyte

[0083] In a glove box filled with nitrogen (O2<1 ppm, H2O<1 ppm), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC) are mixed in a mass ratio of 3:1:1 to prepare 83 g of a non-aqueous organic solvent. Then, 0.5 g of imidazole sulfonate compound A1, 0.5 g of 1,6-hexane diisocyanate, and 1 g of pentaerythritol bis-cyclic sulfate are added as electrolyte additives. Then, 1 g of fluoroethylene carbonate (FEC) and 0.5 g of 1,3-propane sulfonate lactone (PS) are added as auxiliary agents to obtain a mixed solution.

[0084] The mixed solution is sealed, packaged, and placed in a freezer (below 0°C) for 2 h. Then, 13.5 g of sodium hexafluorophosphate is slowly added to the mixed solution in a glove box filled with nitrogen (O2<1 ppm, H2O<1 ppm). After mixing, the electrolyte is prepared. The specific composition of the electrolyte is shown in Table 1.

[0085] (4) Preparation of the sodium ion battery

[0086] The positive electrode sheet, the polyethylene isolation film and the negative electrode sheet are stacked in sequence, and then wound to obtain a battery cell. The tab is welded, the battery cell is placed in an outer package, and electrolyte is injected into the outer package. After packaging, standing, formation and shaping, a sodium ion battery with a theoretical capacity of 1100 mAh is obtained.

[0087] Example 2

[0088] The lithium ion battery of the present embodiment is prepared by a method comprising the following steps:

[0089] (1) Preparation of the positive electrode sheet

[0090] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, the conductive agent carbon black, the carbon nanotube and the binder polyvinylidene fluoride (PVDF) are added into N-methyl pyrrolidone (NMP) in a mass ratio of 96.3:2:0.5:1.2 to prepare a positive electrode slurry;

[0091] The positive electrode slurry is coated on the upper and lower surfaces of the aluminum foil, dried and then cold-pressed. After edge cutting, sheet cutting and striping, the positive electrode sheet is prepared.

[0092] (2) Preparation of the negative electrode sheet

[0093] The graphite, the conductive agent carbon black, the binder styrene butadiene rubber (SBR) and the thickening agent (CMC) are prepared into a negative electrode slurry in deionized water in a mass ratio of 95:1.5:2:1.5;

[0094] The negative electrode slurry is coated on the upper and lower surfaces of the copper foil, dried, and then cold-pressed, edge cut, sheet cut and striped to prepare the negative electrode sheet.

[0095] (3) Preparation of the electrolyte

[0096] In a glove box filled with nitrogen (O2<1 ppm, H2O<1 ppm), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) and ethylene carbonate (EC) are uniformly mixed in a mass ratio of 5:2:3 to prepare 83 g of a non-aqueous organic solvent. Then, 0.5 g of imidazole sulfonate compound A1, 0.5 g of 1,6-hexane diisocyanate and 1 g of pentaerythritol bis-cyclic sulfate are added as additives. Then, 1 g of fluoroethylene carbonate (FEC) and 0.5 g of 1,3-propane sulfonic acid lactone (PS) are added as auxiliary agents to obtain a mixed solution.

[0097] The mixed solution is sealed, packaged and placed in a freezer (below 0°C) for 2 h. Then, 13.5 g of lithium hexafluorophosphate is slowly added to the mixed solution in a glove box filled with nitrogen (O2<1 ppm, H2O<1 ppm). After uniform mixing, the electrolyte is prepared.

[0098] (4) Preparation of lithium ion battery

[0099] The positive electrode sheet, the polyethylene separator, and the negative electrode sheet were stacked in order, and then were wound to obtain a battery cell. The battery cell was welded, placed in an outer package, and injected with electrolyte. After packaging, standing, formation, and shaping, a lithium ion battery with a theoretical capacity of 1500 mAh was obtained.

[0100] Examples 2-28 and Comparative Examples 1-3

[0101] The electrolyte of Examples 2-28 and Comparative Examples 1-3 was substantially the same as that of Example 1, except for the differences shown in Table 1.

[0102] The electrolyte of Example 1 was replaced with the electrolyte of Examples 2-28 and Comparative Examples 1-3, respectively, to obtain secondary batteries of Examples 2-28 and Comparative Examples 1-3, respectively.

[0103] Table 1

[0104] Performance test

[0105] The secondary batteries of the examples and comparative examples were subjected to the following performance tests, and the results are shown in Table 2.

[0106] In the following tests, the charge and discharge cutoff voltage of the sodium ion battery was 1.5 V to 4.2 V, and the charge and discharge cutoff voltage of the lithium ion battery was 2.5 V to 4.5 V.

[0107] 1) High-temperature cycle performance test

[0108] Two secondary batteries completed by partial capacity of the upper clamps were placed in a 45°C temperature environment, and were charged at a constant current and constant voltage to the upper limit cutoff voltage at a current of 1C, and the cutoff current was 0.05C. Then, the secondary batteries were discharged at a constant current to the lower limit cutoff voltage at a current of 1C. This cycle was repeated, and the discharge capacity of the first cycle and the discharge capacity of the 500th cycle of the two secondary batteries were recorded, respectively. The capacity retention rate was calculated according to the following formula.

[0109] Capacity retention rate = discharge capacity of the 500th cycle / discharge capacity of the first cycle x 100%.

[0110] 2) High-temperature storage test

[0111] One of the two secondary batteries completed by the upper clamp split capacity is placed in an environment of 25°C after the clamp is removed, and charged to the upper limit cutoff voltage at a current of 1C, and the cutoff current is 0.05C, and then discharged to the lower limit cutoff voltage at a current of 1C, and the discharge capacity at this time is recorded as C0, and the thickness of the battery cell before high-temperature storage is tested using a battery cell thickness tester, and recorded as D1. Then the battery cell is charged to the upper limit cutoff voltage at a current of 1C again, and the cutoff current is 0.05C, and then the full secondary battery is placed in a 60°C constant temperature oven for 30 days, and then the secondary battery is taken out, and immediately the thickness of the battery cell after high-temperature storage is tested using a battery cell thickness tester, and recorded as D2, and then the secondary battery is placed in an environment of 25°C for 2 hours, and then discharged to the lower limit cutoff voltage at a current of 1C in an environment of 25°C, and the discharge capacity at this time is recorded as C1, and then charged to the upper limit cutoff voltage at a current of 1C, and the cutoff current is 0.05C, and discharged to the lower limit cutoff voltage at a current of 1C. The discharge capacity at this time is recorded as C2.

[0112] Capacity retention rate = (C1 / C0) x 100%; Capacity recovery rate = (C2 / C0) x 100%.

[0113] Thickness expansion rate = (D2-D1) / D1 x 100%.

[0114] 3) High-temperature storage 30d before and after DCIR change rate test

[0115] One of the two secondary batteries completed by the upper clamp split capacity is placed in an environment of 25°C after the clamp is removed, and charged to the upper limit cutoff voltage at a current of 1C, and the cutoff current is 0.05C, and then discharged to the lower limit cutoff voltage at a current of 1C, and the discharge capacity at this time is recorded as C0, and the thickness of the battery cell before high-temperature storage is tested using a battery cell thickness tester, and recorded as D1. Then the battery cell is charged to the upper limit cutoff voltage at a current of 1C again, and the cutoff current is 0.05C, and then the full secondary battery is placed in a 60°C constant temperature oven for 30 days, and then the secondary battery is taken out, and immediately the thickness of the battery cell after high-temperature storage is tested using a battery cell thickness tester, and recorded as D2, and then the secondary battery is placed in an environment of 25°C for 2 hours, and then discharged to the lower limit cutoff voltage at a current of 1C in an environment of 25°C, and the discharge capacity at this time is recorded as C1, and then charged to the upper limit cutoff voltage at a current of 1C, and the cutoff current is 0.05C, and discharged to the lower limit cutoff voltage at a current of 1C. The discharge capacity at this time is recorded as C2.

[0116] Before high-temperature storage: the discharge DC resistance at 50% SOC is calculated according to the following formula: DCIR1(mΩ) = (V0-V1) / (I x 2C) x 1000.

[0117] The secondary battery stored for 30 d was taken out, and after standing for 2 h in an environment of 25 °C, it was discharged at a constant current of 1 C to the lower limit cutoff voltage in an environment of 25 °C, and then charged at a constant current of 1 C to the upper limit cutoff voltage, with a cutoff current of 0.05 C, for 3 cycles, and then discharged at a constant current of 1 C for 30 min, and the discharge voltage V2 at this time was recorded. The secondary battery (such as a sodium ion battery) adjusted to 50% SOC was allowed to stand for 5 min at 25 °C, and discharged at a constant current of 2 C for 30 s, and the discharge voltage at this time was recorded as V3, and the discharge current at 2 C was I1 x 2 C.

[0118] After high-temperature storage for 30 d: the discharge DC internal resistance at 50% SOC was calculated according to the following formula: DCIR2 (mΩ) = (V2-V3) / (I1 x 2C) x 1000.

[0119] The change rate of the DC internal resistance DCIR before and after high-temperature storage for 30 d = (DCIR2-DCIR1) / DCIR1 x 100%.

[0120] Table 2

[0121] As can be seen from Table 2, compared with the comparative examples, the battery of the embodiments of the present disclosure has more excellent high-temperature cycle capacity retention rate, high-temperature storage capacity retention rate, high-temperature storage capacity recovery rate, has a lower high-temperature storage thickness expansion rate and high-temperature storage DCIR change rate, indicating that by including imidazole sulfonate compounds, pentaerythritol bis-cyclic sulfate and 1,6-hexane diisocyanate in the electrolyte additive, the high-temperature cycle performance and high-temperature storage performance of the battery can be improved.

[0122] As can be seen from Example 1 and Example 2, when the electrolyte additive of the present disclosure is applied to a sodium ion battery, it has more excellent high-temperature cycle performance and high-temperature storage performance, and the reason is that compared with a sodium ion battery, the upper limit voltage of a lithium ion battery is too high, which easily causes the cycle performance and storage performance of the battery to deteriorate.

[0123] As can be seen from Example 1, Examples 3-6, when the imidazole sulfonate compound is A1, the obtained battery has more excellent high-temperature cycle performance and high-temperature storage performance.

[0124] As can be seen from Example 1, Examples 7-10, Examples 12-15 and Example 11, by making the mass ratio of imidazole sulfonate compound to 1,6-hexane diisocyanate (0.001-100): 1, the high-temperature cycle performance and high-temperature storage performance of the battery can be improved. Further, as can be seen from Example 1, Examples 7-8, Examples 12-15 and Examples 9-11, by further making the mass ratio of imidazole sulfonate compound to 1,6-hexane diisocyanate (0.05-10): 1, the high-temperature cycle performance and high-temperature storage performance of the battery can be further improved.

[0125] As can be seen from Example 19 and Example 20, by selecting the content of electrolyte additive in the electrolyte, the high-temperature cycle performance and high-temperature storage performance of the battery can be further improved. Further, as can be seen from Example 8 and Example 14, when the content of electrolyte additive in the electrolyte is 0.5-6%, the battery obtained has more excellent high-temperature cycle performance and high-temperature storage performance.

[0126] As can be seen from Example 26 and Example 27, by adding an auxiliary agent to the electrolyte, the high-temperature cycle performance and high-temperature storage performance of the battery can be improved. Further, as can be seen from Example 21 and Example 26, by selecting the content of each component in the electrolyte, the high-temperature cycle performance and high-temperature storage performance of the battery can be further improved.

[0127] Further, as can be seen from Example 1, Examples 23-24 and Example 22, when the content of auxiliary agent in the electrolyte is ≤5%, the high-temperature cycle performance and high-temperature storage performance of the battery can be further improved. As can be seen from Example 24-25 and Example 23, when the content of auxiliary agent in the electrolyte is 0.2-2%, the battery obtained has more excellent high-temperature cycle performance and high-temperature storage performance. As can be seen from Example 22-25 and Example 27, by selecting the content of each component in the electrolyte, the high-temperature cycle performance and high-temperature storage performance of the battery can be further improved.

[0128] As can be seen from Example 1 and Example 28, when the mass percentage content of pentaerythritol bis-cyclic sulfate in the electrolyte additive is 0.3-3%, the battery obtained has more excellent high-temperature cycle performance and high-temperature storage performance.

[0129] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, and are not intended to limit the present disclosure; although the present disclosure has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. An electrolyte additive, comprising an imidazole sulfonate compound, a pentaerythritol bis-cyclic sulfate, and 1,6-hexane diisocyanate.

2. The electrolyte additive according to claim 1, wherein, The imidazole sulfonate compound includes a compound represented by Formula 1. In formula 1, R1is selected from the group consisting of hydrogen, substituted or unsubstituted C6-C18 aryl, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted thienyl, substituted or unsubstituted imidazolyl, substituted or unsubstituted pyridyl, a group represented by formula 2; In formula 2, R2, R3, R4 are each independently selected from hydrogen, halogen, substituted or unsubstituted C1-C10 alkyl.

3. The electrolyte additive according to claim 2, wherein, R1 is selected from hydrogen, phenyl, thienyl, imidazolyl, pyridyl, fluorophenyl, fluorothienyl, fluorimidazolyl, fluoropyridyl, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl, 2-butyl, fluoromethyl, fluoroethyl, fluoro-1-propyl, fluoro-2-propyl, fluoro-1-butyl, fluoro-2-methyl-1-propyl, fluoro-2-butyl, vinyl, propenyl, butenyl, fluorovinyl, fluoropropenyl, fluorobutenyl, trimethylsilyl, triethylsilyl, trifluorosilyl, (trifluoromethyl)dimethylsilyl, di(trifluoromethyl)methylsilyl, tri(trifluoromethyl)silyl, silanophenyl.

4. The electrolyte additive according to claim 2 or 3, wherein, The imidazole sulfonate compound is selected from the group consisting of compounds represented by the following structures:

5. The electrolyte additive according to any one of claims 1 to 4, wherein, In the electrolyte additive, the mass ratio of the imidazole sulfonate compound to the 1,6-hexane diisocyanate is (0.001-100):

1.

6. The electrolyte additive according to any one of claims 1 to 5, wherein, The mass ratio of the imidazole sulfonate compound to 1,6-hexane diisocyanate is (0.05-10):

1.

7. The electrolyte additive according to any one of claims 1 to 6, wherein, In the electrolyte additive, the mass percentage of the pentaerythritol bis-cyclic sulfate is 0.3%-3%.

8. An electrolyte, comprising the electrolyte additive of any one of claims 1-7.

9. The electrolyte of claim 8, wherein, In the electrolyte, the mass percentage of the electrolyte additive is 0.36%-18%.

10. The electrolyte of claim 9, wherein, In the electrolyte, the mass percentage of the electrolyte additive is 0.5%-6%.

11. The electrolyte of any one of claims 8-10, wherein, The electrolyte further comprises an electrolyte salt and a solvent. The electrolyte comprises, by mass percentage: 7%-18% of the electrolyte salt, 65%-88% of the solvent, 0.01%-5% of the imidazole sulfonate compound, 0.05%-10% of the 1,6-hexane diisocyanate, and 0.3%-3% of the pentaerythritol bis-cyclic sulfate.

12. The electrolyte of any one of claims 8-11, wherein, The electrolyte further comprises an auxiliary agent. The auxiliary agent is selected from at least one of 1,3-propane sulfonic acid lactone, 1,3-propene sulfonic acid lactone, fluorinated ethylene carbonate, bis-fluorinated ethylene carbonate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, triphenyl phosphate, triphenyl phosphite, succinic anhydride, dimethyl maleic anhydride, and methylene methane disulfonate.

13. The electrolyte of claim 12, wherein, In the electrolyte, the mass percentage of the auxiliary agent is ≤5%.

14. The electrolyte of claim 12 or 13, wherein, The electrolyte comprises, by mass percentage: 9%-15% of the electrolyte salt, 75%-86% of the solvent, 0.1%-1% of the imidazole sulfonate compound, 0.1%-2% of the 1,6-hexane diisocyanate, 0.3%-1% of the pentaerythritol bis-cyclic sulfate, and 0.2%-2% of the auxiliary agent.

15. A secondary battery, comprising the electrolyte of any one of claims 8-14.

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